1. Field of the Invention
The invention relates generally to an electronically monitored mechanical pipette. More specifically, the invention relates to an electronically monitored volume delivery adjustment mechanism for a pipette. Even more specifically the invention relates to a microswitch for signalling the electronic system of an electronically monitored mechanical pipette when volume setting adjustment is taking place.
2. Prior Art
Mechanically operated micropipettes are well known in the art as exemplified by U.S. Pat. No. 4,909,991 to Oshikubo. In such prior art devices, the volume of liquid to be dispensed by the pipette is generally indicated to the operator by means of a mechanical display. The display commonly consists of a set of rotary drums driven by a gear mechanism attached to the actuating shaft of the pipette, such that rotation of the actuating shaft causes the drums to rotate to display a new setting. However, due to unavoidable mechanical wear and tear on pipettes, the amount of fluid actually being delivered by a pipette may not actually correspond to the volume being indicated by the mechanical displayed. Further, accuracy may degrade over time as the actuating elements, such as the shaft, gears, and rotary drum, wear out.
Electrically driven pipettes are also well known in the art as exemplified by U.S. Pat. No. 4,905,526 to Magnussen, Jr. et al. This type of instrument commonly includes an electronic display for displaying the volume of fluid to be dispensed by the pipette, and an actuator generally comprised of an electric drive mechanism, such as a stepper motor. The stepper motor generally drives a rotor, which is attached by a threaded screw to an actuator shaft, the threaded screw changes the rotational motion of the motor into linear motion of the actuator shaft. The shaft thereafter drives a piston to displace fluid for pipetting. Although electrically operated pipettes have some advantages over mechanically operated pipettes, they nevertheless suffer from several drawbacks. First, the enlarged size of an electrically operated pipette, due to the need to accommodate the electric driving mechanism, and the added electronic hardware, make the device very difficult to handle for the operator. Further, the electronic motor can be very power demanding and thus necessitate connection of the pipette to a power source, or the use of large batteries which can be rapidly drained of power.
Electrically monitored mechanical pipettes are also known in the art as exemplified by U.S. Pat. No. 4,567,780 to Oppenlander et al. This type of instrument generally includes a plunger having an adjustable stroke length which is generally adjusted by rotating the plunger itself. The electrical monitoring system monitors plunger rotation and electronically displays the volume delivery setting corresponding to the plunger position. The device continuously monitors the plunger position and volume delivery setting of the pipette. Although this device overcomes several of the disadvantages of mechanical and electrical pipettes, it nevertheless fails to completely resolve the problem of high power demands during operation.